EPH family receptor protein-tyrosine kinases and ephrin ligands play important roles in neural and cardiovasular development. Our recent study has shown that high-level expression of EPHB6, ephrin-B2, and ephrin-B3 predicts favorable disease outcome of neuroblastoma (NB), a common pediatric tumor of neural crest origin. The goal of this study is to elucidate the underlying mechanisms by which EPHB6, ephrin-B2, and ephrin-B3 provide NB cells with favorable phenotype. EPHIB6 lacks its kinase activity due to a mutation at the ATP acceptor site. Ephrin-B ligands are bi-functional molecules in that their extracellular domains promote angiogenesis and their cytoplasmic domains suppress the growth-promoting activity of activated protein-tyrosine kinases. Based on these observations, we hypothesize that EPHB6 restricts growth, angiogenesis and metastasis of NB cells by acting as a dominant negative member among the EPHB receptor family and/or by sequestering ephrin-B ligands from participating in angiogenesis. Cytoplasmic domains of ephrin-B ligands may inhibit NB growth by suppressing the growth stimulatory effect of receptor tyrosine kinases (IGF1R and TrkA) that are highly expressed by favorable NB. To test these hypotheses, we will examine whether EPHB6 restricts growth, angiogenesis and metastasis of NB cells. We will also examine whether extracellular domains of ephrin-B2 and ephrin-B3, in the absence of EPHB6, facilitate angiogenesis and metastasis of NB and whether EPHB6 blocks the action of ephrin-B ligands in facilitating these processes. We will investigate whether cytoplasmic domains of ephrin-B2 and ephrin-B3 suppress the growth promoting activity of IGF1R and TrkA. Lastly, we will examine whether inhibitors of DNA methylation and histone deacetylation increase EPHB6, ephrin-B2, and ephrin-B3 expressions in unfavorable NB cells, and if so, how these changes affect growth, angiogenesis and metastasis of unfavorable NB cells. Results of this study would reveal novel mechanisms by which EPHB6 and ephrin-B ligands restrict growth, angiogenesis and metastasis of NB. Such knowledge may help develop an innovative and effective treatment for unfavorable NB.